In the past, packers and other downhole tools have been provided with emergency-release mechanisms to facilitate retrieval of the downhole tool when conditions made that operation necessary. Baker Hughes Incorporated, through its Baker Oil Tools division, has offered shear-release packers with the shearing mechanism rated in the order of about 20,000-30,000 lbs. Other types of tools have been provided that use a sliding sleeve mechanism or collet ring to effectuate the release. In these types of designs, the release mechanism is functional when a sleeve is shifted by shifting tools of known design to undermine a collet, thereby allowing the packer or anchor to be retrieved. One type of device that uses this type of a sliding sleeve mechanism for locking and unlocking a downhole tool in position is a Baker Oil Tools Model SW, Wireline-locked, Parallel Snap Latch Seal Nipple, Product No. 707-60.
The prior designs, employing solely a shear-release mechanism, did not present a design that was suitable for wells where stimulation or acidizing were to occur. Similarly, if tubing-conveyed perforating guns were to be used, shear releases were not desirable. The reason for this was the potentiality of premature shear release when such activities were occurring. In shooting off tubing-conveyed perforating guns, the forces that could be generated could well exceed the typical range of shear forces designed into a release mechanism. Commonly, shear forces in the order of 50,000 lbs. could be generated in firing tubing-conveyed perforating guns, while certain stimulation procedures could generate shear forces on the shear-release mechanism as high as 90,000 lbs. The prior designs, using a shear-release mechanism, generally had the rated release force at considerably less than the forces that could be generated during perforating or formation treatment as described above. As a result, operators have elected not to use shear-release packers when performing such procedures. It was determined to be undesirable to raise the shear rating on the shear-release member to the levels of shear force anticipated during perforating or formation stimulation because raising the shear force required for release presented other problems when it came time to actually retrieve the packer. Normally, it was desirable to have as low a shear force as possible to facilitate the subsequent retrieval of the packer in normal operations. At the same time, it was also desirable to have a packer or other downhole tool that could withstand the forces generated during perforating or formation treatment.
Well operators, when needing to do perforating or stimulation or acidizing, have then moved to wireline-releasable packers in lieu of the shear-release mechanisms. This approach was serviceable as long as the well was not of the type that developed paraffin scale or where corrosion could attack the mechanism and make it difficult to trip with a wireline. In the design that employed only a shifting sleeve or ring mechanism to effectuate locking or release, the packer or other downhole tool would be locked into position while the subsequent operations would take place. The problem arose because there could be a very long period of time between when the perforation or formation treatment such as acidizing took place and when it then became necessary to remove the packer. In the interim period, the environmental conditions downhole could have worked on the shifting mechanism to the degree that it became unserviceable. Such mechanisms could so thoroughly jam or in other ways become mechanically nonfunctional so as to require more drastic operations to remove the packer, such as milling.
One of the objects of this invention is to make it possible for operators to position and secure a downhole tool so that operations which generate high loadings could immediately take place without fear of premature shear release. Furthermore, to further the objectives of the invention, the short-term advantages of being able to withstand high shear loadings could be provided in the invention, while at the same time the long-term disadvantages due to environmental attack could then be eliminated by enabling a shear-release mechanism long before any of the environmental conditions could disable the moving sleeve release mechanism or an equivalent which had been relied on during the perforating or acidizing or other formation treatment operations.